This invention relates to processes for producing di(nitrophenyl) ethers and the purification of crude di(nitrophenyl) ether reaction products. More particularly, di(nitrophenyl) ethers are prepared by the reaction of a halogeno-nitrophenyl compound with a base wherein the water in the reaction system is removed during the reaction. The use of two different temperatures during the reaction is advantageous. The yield of di(nitrophenyl) ether is improved by the use of a molar excess of halogeno-nitrophenyl compound. Purification is performed by extraction into a non-aqueous solvent using a dual temperature method.
Di(nitrophenyl) ethers have been prepared from the reaction of alkali metal nitrophenolates and certain halogeno-nitrobenzenes by the Williamson synthesis. Di(nitrophenyl) ethers may be subsequently hydrogenated to form diamino-diphenyl ethers. The diamino-diphenyl ethers are useful as bifunctional cross-linking network-extending agents for various polymers. In particular, bis(para-nitrophenyl)ether is hydrogenated to oxybis(aniline) which in turn is used as a monomer to produce high molecular weight polymers, e.g., amide-imide terpolymers.
Diamino-diphenyl ethers have been prepared by the condensation of halogeno-mononitrobenzene with an alkali metal nitrophenate in a solvent such as dimethylacetamide by Spiegler in U.S. Pat. No. 3,192,263. However, there are several disadvantages in preparing the ether by using an alkali metal nitrophenate as a starting material. First, the nitrophenate is prepared separately by reaction of a halogeno-nitrobenzene and a base. After the reaction, the unreacted halogeno-nitrobenzene is removed some means, e.g., steam distillation. Such a process of removal can be extremely hazardous since the nitrophenate may explode at high temperatures.
A process which involves the in situ formation of the alkali metal nitrophenate by the reaction of a base with a halogeno-nitrobenzene has been disclosed by Bentz et al. in U.S. Pat. No. 3,634,519. The reference teaches the production of 4,4'-dinitro-diphenyl ethers by the condensation of a 1-halo-4-nitrophenyl compound with an aqueous solution of an alkali metal hydroxide wherein the molar ratio of phenyl compound to alkali metal hydroxide is between 1:1 and 1:1.1, i.e., a slight excess of hydroxide is used in the reaction.
The object of this invention is to provide improved methods of conducting the reaction of a base with a halogeno-nitrophenyl compound which avoids the problems associated with handling the nitrophenate and significantly improves the selectivity to and yield of di(nitrophenyl) ether with reduced formation of undesirable by-products. A further object of this invention is to provide a method of purifying crude di(nitrophenyl) ether reaction products by an extraction method which reduces the amount of impurities in the final product and avoids costly and inconvenient solids handling operations.